1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a method for fabricating an LCD having a liquid crystal dropping method applied thereto.
2. Discussion of the Related Art
In general, recent developments in the information communication field have increased demand for various types of display devices. In response to this demand, various flat panel displays such as liquid crystal display (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent display (VFD) have been developed, some of which have been employed as displays in various products.
The LCDs have been used most widely as mobile displays while the LCD replaces the CRT (Cathode Ray Tube) because of features and advantages including excellent picture quality, light weight, thin profile, and low power consumption. In addition to the mobile type LCDs, such as a display for notebook computer, LCDs have been developed for computer monitors and televisions to receive and display broadcasting signals.
Despite various technical developments in the LCD technology with applications in different fields, research in enhancing the picture quality of the LCD as a display has been in some respects lacking as compared to the features and advantages of the LCD. Therefore, to use the LCD in various fields as a general display, the key to developing the LCD lies on whether the LCD can implement a high quality picture, such as high resolution, high luminance, and large sized screen while still maintaining light weight, thin profile, and low power consumption.
The LCD is provided with a liquid crystal panel for displaying a picture, and a driving part for providing a driving signal to the liquid crystal panel. The liquid crystal panel has first and second glass substrates bonded together with a gap between the substrates. A liquid crystal layer is formed by injecting liquid crystal between the first and second glass substrates.
On the first glass substrate (a TFT array substrate, for example), there are a plurality of gate lines arranged in a first direction at fixed intervals, a plurality of data lines arranged in a second direction perpendicular to the gate lines at fixed intervals, a plurality of pixel electrodes in respective pixel regions defined by the gate lines and the data lines in a matrix, and a plurality of thin film transistors switchable in response to a signal from the gate lines for transmission of a signal from the data line to the pixel electrodes.
The second glass substrate (a color filter substrate) has a black matrix layer for shielding light from areas excluding the pixel regions, red (R), green (G), blue (B) color filter layers, and a common electrode for implementing a picture.
The foregoing first and second substrates have a gap between them which is maintained by spacers, and bonded by a sealant. The seal has a liquid crystal injection inlet through which liquid crystal is injected after the two substrates are bonded and sealed.
After the individual liquid crystal panels are cut, the space between the two bonded substrates of each LCD panel is evacuated and the liquid crystal injection inlet is dipped in a liquid crystal bath, so that the liquid crystal is injected into the space by a capillary tube phenomenon. Once the liquid crystal is injected into the space between the two substrates the liquid crystal injection inlet is sealed by a sealant.
However, the related art method for fabricating an LCD having liquid crystal injected therein has the following problems. First, the related art method has poor productivity because the dipping of the liquid crystal in a liquid crystal bath while the space between the two substrates are maintained at a vacuum and the unit panels are cut into individual pieces for injection of the liquid crystal takes much time. Second, the liquid crystal injection, for a large LCD in particular, may cause imperfect filling of the liquid crystal in the panel, which may result in a defective panel. Third, the complicated and lengthy fabrication process requires the use of many liquid crystal injection devices, which occupies a large portion of space.
Accordingly, a method for fabricating an LCD by using a liquid crystal dropping method has been under research recently. Japanese Patent Application Nos. H11-089612, and H11-172903, and Japanese Laid-Open Patent Publication No. 2000-147528 disclose the following liquid crystal dropping method.
A related art method for fabricating an LCD having the foregoing liquid crystal dropping method applied thereto will be explained. FIGS. 1A–1F illustrate steps of a related art method for fabricating an LCD.
Referring to FIG. 1A, UV seal 1 is coated on a first glass substrate 3 having a thin film transistor array formed thereon to a thickness of approximately 30 μm, and liquid crystal 2 is dropped on an interior of the seal 1 which is the thin film transistor array part. No liquid crystal injection opening is provided in the seal 3.
The first glass substrate 3 is mounted on a table 4 in a vacuum container ‘C’ which is movable in a horizontal direction, and held by a plurality of first vacuum holes 5 on the entire bottom surface of the first glass substrate 3.
Referring to FIG. 1B, the bottom surface of the second glass substrate 6 having a color filter array formed thereon is held by vacuum using a second plurality of vacuum holes 7. The vacuum container ‘C’ is closed and evacuated. The second glass substrate 7 is moved downward in a vertical direction until a gap between the first glass substrate 3 and second glass substrate 6 is 1 mm. The table 4 supporting the first glass substrate 3 thereon is moved in a horizontal direction, to align the first and second glass substrates 3 and 6.
Referring to FIG. 1C, the second glass substrate 6 is moved downward until the second glass substrate 6 comes into contact with the liquid crystal 2 or the sealant 1. Referring to FIG. 1D, the table 4 with the first glass substrate 3 thereon is moved in a horizontal direction to align the first and second glass substrates 3 and 6. Referring to FIG. 1E, the second glass substrate 6 is moved further down until the gap between the second glass substrate 6 and the first glass substrate 3 becomes 5 μm.
Referring to FIG. 1F, the pre-bonded first and second glass substrates 3 and 6 are taken out of the vacuum container ‘C’, and a UV ray is directed to the sealant, to set the sealant 1, thereby completing the fabrication process.
However, the foregoing related art method for fabricating an LCD having the liquid crystal dropping method applied thereto has the following problems.
First, coating the sealant and dropping the liquid crystal on the same substrate requires much fabrication time before the two substrates can be bonded to each other.
Second, as the seal is coated and the liquid crystal is dropped on the first substrate while the second substrate sits idle, there is an unbalance of a fabrication process between the first and second substrates, resulting in an ineffective operation of the production line.
Third, because the seal is coated and the liquid crystal is dropped on the first substrate, the first substrate with a coat of the sealant applied thereto can not be subjected to cleaning by a USC. Therefore, as the sealant that will bond the two substrates should not be removed, undesirable particles also cannot be removed, which may cause defective contact of the sealant in the bonding.
Fourth, since the bonding of the two substrates is done by the table and the second plurality of vacuum holes, there is a possibility of defective bonding caused by nonuniform application of pressure throughout the substrate when the levels of the table and the second plurality of vacuum holes are not accurate.
Fifth, the introduction of air into the vacuum container when the vacuum container is pressurized to the atmospheric pressure may deteriorate the integrity of the vacuum container due to moisture contained within the air.